Conventionally, coil components such as inductors, transformers, chokes, and motors are used in a wide variety of applications such as home electric appliances, industrial apparatuses, and vehicles. A common coil component includes a magnetic core and a coil wound around the magnetic core in many cases. For such a magnetic core, ferrite is widely used, which is excellent in magnetic properties, a degree of freedom of a shape, and cost merits.
In recent years, as a result of downsizing of power supplies for electronic devices or the like, there has been a strong demand for compact low-profile coil components which can be used even with a large current. Magnetic cores containing a metal-based magnetic powder which has a saturation magnetic flux density higher than that of ferrite are increasingly used.
As the metal-based magnetic powder, Fe—Si-based, Fe—Ni-based, Fe—Si—Cr-based, and Fe—Si—Al-based magnetic alloy powders are used, for example. A magnetic core obtained by consolidating a green compact of the magnetic alloy powder has a high saturation magnetic flux density. But, the magnetic core has low electric resistivity because of the alloy powder. The magnetic alloy powder is previously insulation-coated with water glass or a thermosetting resin or the like in many cases.
Meanwhile, the following technique has also been proposed (see Patent Document 1). Soft magnetic alloy particles containing Al and Cr together with Fe are molded, and then heat-treated in an oxygen-containing atmosphere to form an oxide layer obtained by the oxidation of the alloy particles on the surface of the particles. The soft magnetic alloy particles are bonded via the oxide layer, and insulation properties are imparted to a magnetic core.